HPS4 and Hermansky-Pudlak syndrome: Genotype-phenotype correlations exist in HPS, where individuals with deficiencies in the biogenesis of lysosome-related organelle complex (BLOC), e.g., BLOC-2 deficiency (caused by HPS3, HPS5, or HPS6) display milder symptoms (such as minimal iris transillumination, fundus hypopigmentation, cutaneous involvement, and visual acuity as good as 0.4 LogMAR) than those with BLOC-3 deficiency (caused by HPS1 or HPS4) [74].